A MEMS device is a blending of integrated circuit (IC) technology with micro-sized mechanical elements. As a result, MEMS devices combine ICs with three-dimensional features and even moving parts. The electronics of a particular MEMS device is typically fabricated using integrated circuit (IC) fabrication techniques, while the micro-mechanical components are typically fabricated using micro-machining processes.
Within the field of MEMS generally, there continues to be a high demand for new “on-chip,” planar micro-machined inductors that exhibit high inductance and possess a high quality factor (i.e., the Q-factor or, more simply, Q). The demand has been driven in large part by the advent of magnetic driving MEMS applications, such as magnetic microactuators and micro-sensors as well as miniature integrated power converter devices. The requirements for these and similar such devices include small size, low loss, large inductance, high current-carrying capacity, and low fabrication costs.
The goal of devising effective and efficient fabrication techniques for such devices in a planar geometry has proved a difficult challenge, presenting problems that continue to be obstacles to the implementation of low-cost, fully-integrated magnetic MEMS devices. Moreover, utilization of such MEMS devices has been limited due to the relatively low inductance that is conventionally achieved with such devices, the inductance being typically on the order of a few to several hundred nano-henries (nH).
Accordingly, despite numerous MEMS inductor designs, utilization of existing devices continues to be largely confined to high-frequency regimes such as RF and microwave circuits as well as signal processing circuits. This is due to the low inductance, low Q factor, and poor power handling capacity typically exhibited by the conventional devices resulting from conventional fabrication processes.
In accordance with conventional fabrication techniques, MEMS inductors are made by etching a substrate or flipping up to reduce substrate loss. The robustness and high-vibration sensitivity of suspended thin-film inductors fabricated according to these techniques can pose problems, however. Some proposed solutions entail using thick photolithography to create thick conductor layers so as to reduce series resistance, but the stability and reliability of the employed polymers are still concerns. The remaining problem of substrate loss can pose yet another problem.
Conventional techniques, moreover, do not provide for effective and efficient fabrication of power electronic devices, in which inductance usually must be high—in the range of 100 nano-henries (nH) to a few micro-henries (μH)—and current-carrying capacity typically must be considerable—in the range of 10 Amperes (A). Resistance is typically in the range of a few milliohms (mΩ) range. In addition, conventional fabrication techniques for such devices tend not to be IC compatible. Thus, application-specific ICs and chip-to-chip wire bondings are often needed to effect fabrication of such devices, typically resulting in increased cost and performance degradation.
It follows that there remains a need for effective and efficient processes for fabricating IC-compatible MEMS inductors and similar devices that possess high Q factors, high inductance, and high current-carrying capacity.